1. Field of the Invention
The present invention relates to a liquid crystal display control circuit, and particularly to a liquid crystal display control circuit for driving a liquid crystal display using a high power mode and a low power mode.
2. Description of Related Art
Recently, liquid crystal displays are widely used for portable information equipments such as cell phone and notebook computer. In portable information equipment, reduction in power consumption for longer battery duration is strongly desired. Along with an improvement of processing speed in portable information equipments, high quality display capability is demanded having more display colors and pixels. Display panel such as TFT (Thin Film Transistor) with pixels arranged in matrix are used to satisfy such demand.
In a liquid crystal panel, an image is displayed on a display area by a driver unit of a liquid crystal display control circuit applying a voltage corresponding to a picture signal onto the display area (display unit) including a capacitive load. FIG. 7 is a view showing a liquid crystal panel and its driver unit according to a conventional technique. In order to display a high quality image, voltages for pixels must be switched at high speeds. Accordingly a large current capacity is required for the driver unit in a liquid crystal display control circuit of a liquid crystal panel so as to drive the parasitic capacitance fast. However providing large current capability on a driver unit introduces a problem of increasing a power consumption of the driver unit. To overcome this problem, a technique for lowering a power consumption of the driver unit is disclosed in Japanese Unexamined Patent Application Publication No. 2004-117742.
A technique disclosed in Japanese Unexamined Patent Application Publication No. 2004-117742 provides large current capacity to a driver unit during a period in which a large charge/discharge current is required at a start of driving, in a case of driving pixels in a liquid crystal display (such condition is hereinafter referred to as high power mode). Contrarily in a period in which voltages for pixels are somewhat stable and a large charge/discharge current is not required, current capacity for the driver unit is reduced (such condition is hereinafter referred to as low power mode). Switching between high power mode and lower power mode is carried out by a driver control signal from outside. This is how a reduction of unnecessary current and thus low power consumption is achieved by appropriately changing the current capacity of the driver unit.
In liquid crystal displays generally, switching of display mode such as the number of display pixels or switching to a partial mode for restricting a display area is performed. If the display mode is changed, a switch timing for switching between high power mode and low power mode in the driver unit may need to be altered as well.
In such a case, a conventional liquid crystal display control circuit stores outside a switch timing for switching between high and low power modes for the driver unit depending on the display mode. An appropriate stored timing needs to be selected to be used depending on the display mode.
However it has been discovered that prepared display modes may not be able to cover all display modes even if a setting for mode change of a driver unit is prepared in advance in accordance with display modes, because the display mode is often changed by a user specification.